1. Field of the Invention
The present invention relates in general to optical communications, particularly to optical data communication networks for distributing signals to a plurality of user apparatuses, and specifically to devices for optical fiber connection, e.g. for connecting optical cables to opto-electronic devices adapted to perform electro-optical conversion.
2. Description of Related Art
Currently, in the field of telecommunications, optical technology is mainly used for long-distance transmission of optical signals, taking advantage of the wide band offered by optical fibers. Electrical cables, such as coaxial cables or cables consisting of copper pairs, are instead still predominantly used for the transmission of signals (in a wide range of applications like digital television, telephone, data exchange accomplished via dial-up or xDSL Internet connection) from and towards end users and the exchange of data between electronic appliances (such as personal computers, printers, storage devices) of a Local Area Network (LAN).
However, electrical cables have a relatively narrow bandwidth, and are becoming a limiting factor against the achievement of high transmission rates. Moreover, electrical cables raise problems of electromagnetic interference and impedance matching. Furthermore, electrical cables are relatively stiff, and thus are difficult to insert into the suitable raceways of a building (which, for electrical safety requirements, are to be distinct from the raceways used for the distribution of electrical energy), and, due to their bulkiness, the number of cables that can be inserted in the raceway is limited.
Research interest is therefore steering towards the possibility of using optics not only in the long-distance signal transmission, but also in local networks for distributing signals to a plurality of user apparatuses, for example in a residential building or in an office.
Fiber optic cables have a very large bandwidth, low attenuation values and are essentially transparent to the bit rate, the format and the transmission code; additionally, fiber optic cables are not bulky, rather they are flexible, light, free from electromagnetic interference and have low bending losses; moreover, they can be inserted in the same raceways used for the distribution of electrical energy.
However, for the connection to electronic appliances, fiber optic cables require the use of opto-electronic devices, i.e. devices adapted to perform an optical-to-electrical, or, conversely, an electrical-to-optical conversion, so as to convert the optical signals into corresponding electrical signals, and vice-versa. The conversion of an optical signal into a corresponding electrical signal is conventionally carried out through a photo-detector, whereas the conversion of an electrical signal into a corresponding optical signal is conventionally carried out by an opto-electronic device including a light source, e.g. a laser, emitting light whose intensity can be modulated according to the information transported by the electrical signal.
The connection of an optical fiber to a light source and/or to a photo-detector is conventionally carried out through an optical connector. Typically, an optical connector is a device comprising two parts that can be releasably connected to each other and that must be attached one to an end of the optical fiber, and the other one to a pig-tail of the light source or of the photo-detector.
For example, the installation of an optical cable comprising an optical fiber, suitable for example for setting up a (unidirectional) point-to-point link within a building, between a user electronic appliance and a distribution unit (located, for example, in an office or apartment and, respectively, in the cellar or loft) requires (in addition to the passage of the optical cable along a suitable raceway of the building, from the cellar/loft to the office/apartment): cutting the optical cable to the necessary length; peeling off the optical cable jacket, applying the optical connectors to the two ends of the optical fiber, respectively at the user appliance and at the distribution unit; possibly, applying optical connectors to the light source and to the photo-detector (in the case in which the light source and the photo-detector are not already equipped with connectors); and, finally, connecting, through the connectors, one end of the fiber to the light source, and the other end of the fiber to the photo-detector, respectively at the distribution unit and at the user appliance side, or vice versa; the operations are to be repeated twice in case of a bidirectional link.
An alternative known technique for connecting an optical fiber to an opto-electronic device is by means of a fused junction between an end of the optical fiber and a pigtail of the opto-electronic device.
However, using optical connectors and fused junctions is cumbersome and critical operations are necessary that involve fiber stripping (i.e., removal of the protective outer fiber coating), cleaving and polishing operations, which are very delicate to carry out on site, require high precision (tolerances are in the range of micrometers), and have to be executed by highly specialized personnel, using special tools. All this increases the installation time and costs. Moreover, it often happens that these complex operations have to be carried out in inconvenient and narrow spaces (for example, under a table or desk), increasing the risk that the optical fiber connection is not accomplished with the necessary precision, with the consequence that the link performance strongly reduces.
Therefore, despite their several advantages, the use of fiber optic cables in networks for distributing signals to a plurality of end users has up to now been highly limited both due to the high installation costs and because the optical connection may be unreliable if the aforementioned operations are not carried out correctly.
Thus, there is a strong need of simplifying the installation of a fiber optic network for distributing signals to a plurality of users, ensuring a high degree of reproducibility and limiting the installation costs.